The present invention relates to a novel technique for upgrading lower olefins, including ethene and other C.sub.2 -C.sub.8 aliphatic hydrocarbons, to liquid products by catalytic reaction over a shape selective medium pore acid zeolite at elevated temperature. In particular, it relates to methods and apparatus for converting an ethene-rich feedstock in a multi-stage reactor system.
Recent developments in zeolite catalysts and hydrocarbon conversion processes have created interest in utilizing olefinic feedstock, for producing C.sub.5.sup.+ gasoline, diesel fuel, etc. In addition to the basic work derived from ZSM-5 type zeolite catalysts, a number of discoveries have contributed to the development of new industrial process. This process has significance as a safe, environmentally acceptable technique for utilizing feedstocks that contain lower olefins, especially C.sub.2 -C.sub.5 alkenes. In U.S. Pat. Nos. 3,960,978 and 4,021,502, Plank, Rosinski and Givens disclose conversion of C.sub.2 -C.sub.5 olefins, alone or in admixture with paraffinic components, into higher hydrocarbons over crystalline zeolites having controlled acidity. Garwood, et al. have also contributed improved processing techniques, as in U.S. Pat. Nos. 4,150,062, 4,211,640 and 4,227,992. The above-identified disclosures are incorporated herein by reference.
Conversion of lower olefins, especially propene and butenes, over HZSM-5 is effective at moderately elevated temperatures and pressures. The conversion products are sought as liquid fuels, especially the C.sub.5.sup.+ aliphatic and aromatic hydrocarbons. Operating details for typical oligomerization units are disclosed in U.S. Pat. Nos. 4,456,779; 4,497,968 (Owen, et al.) and No. 4,433,185 (Tabak), incorporated herein by reference.
In the process for catalytic conversion of olefins to heavier hydrocarbons by catalytic oligomerization using an acid crystalline zeolite, such as ZSM-5 type catalyst, process conditions can be varied to favor the formation of either gasoline or distillate range products. At moderate temperature and relatively high pressure, the conversion conditions favor distillate range product having a normal boiling point of at least 165.degree. C. (330.degree. F.). Lower olefinic feedstocks containing C.sub.2 -C.sub.6 alkenes may be converted selectively; however, the low severity distillate mode conditions do not convert a major fraction of ethene. While propene, butene-1 and others may be converted to the extent of 50% to 95% in the distillate mode, only about 10% to 30% of the ethylene component will be converted. It is an object of the present invention to provide a new technique for upgrading ethene-rich feedstocks to liquid hydrocarbons employing an efficient multi-stage system wherein at least one reactor zone includes a metallic ethene oligomerization catalyst component.